How can you configure the first leg of RingOut call to ring both Desk phone and Softphone?

Can you clarify how you call RingOut in this case? What numbers you are specifying as "from" and "to"?

If you go to service.ringcentral.com, do you see that "DirectNumber" is assigned to your desk phone? In this case such behavior is expected. For direct numbers with attached line (device), RingOut routes the call directly to this device (all rules are bypassed). And, you are right, this behavior differs from regular incoming call where call passes through all defined rules.

If you want all your phones to ring in case of RingOut, you should specify direct number not assigned to any device or company number + extension (like +18001234567*102). 

But keep in mind, that there is one disadvantage of such approach: your second leg will start connecting before you actually pick up the first leg (internally call is answered by answering machine which plays announcements, starts finding you according to defined rules, etc). So the use you are calling to might pick up call earlier than you and hear your automated greetings. 

17165083812

Then, as per your discussion, I experimented with +18885225975*126

Yes, using +18885225975*126 worked as you described, but the "to" number was ringing first. I don't like that behavior.

The forwardingNumberId seems like it will be my solution. Difficult to test in the sandbox, as there is no hardphone coexisting with a softphone. I can validate it does connect to the softphone.

Thank you very much.